Top couplings: ILC-B physics interplay Top couplings: ILC-B physics interplay TYL-FJPPL B physics TYL-FJPPL B physics February 20, 2015 LAL February 20, 2015 LAL F. Richard February François Richard LAL/Orsay

Introduction  Top EW couplings direct measurements can only be carried at HE colliders like ILC and LHC  This talk discusses indirect measurements at B factories and at LEP1/SLC (T observable)  I will compare the accuracies which are reachable with these various set ups F. Richard February 20152

LHC  ATLAS and CMS are reaching an accuracy of a few % on Vtb e.g. CMS gives |V tb |=0.998±0.0038(exp.)±0.016(theo.)  If one assumes a SM CKM with V tb ~1 this is translated into a constraint on the WbLtL coupling which, under mild assumptions, can be related to ZtLtL and ZbLbL (measured precisely at LEP1)  Knowing ZtLtL one can use the ttZ cross section to extract ZtRtR  Unfortunately this cross section is known to ±35% and since ZtRtR²/ZtLtL²~0.2, this measurement is insensitive to ZtRtR and this will remain true for long since this measurement is systematics limited to ~5% which corresponds to an error of ~15% on ZtRtR F. Richard February 20153

ILC  ILC produces top quarks through  and Z exchange  Using polarized beams one can separately extract Z axial and vector couplings and the photon coupling (neglecting tensorial terms)  4 observables are available : tt and AFBt for the two polarisations  ILC operates at 500 GeV centre of mass well above tt threshold to avoid large coulombic QCD corrections and to keep good sensitivity to the axial term  Statistical accuracies are overwhelmingly good, beyond theoretical present uncertainties, specially EW corrections F. Richard February 20154

Comparisons LHC ILC  The very large errors at LHC are due to the sign uncertainty which is absent at ILC due to Z- interference  The tensorial terms F2V is obtained assuming SM vectorial terms  F2A can be independently measured by measuring CPV distributions  I will concentrate on Z couplings F. Richard February 20155

Top coupling through loops  The B factory cleanest mode seems to be:  Depends on WbLtL and ZtLtL  The T parameter also depends on top loops  In both cases beware that additional BSM loops (heavy quarks, Z’) can also contribute F. Richard February 20156

EFT  From one writes  T=  SU(2)L gives  There are only 2 EFT parameters simply related to gL and gR Truly most general ?  Looking at concrete BSM models, I believe that this not the case F. Richard February 20157

Results  As expected B physics red band is almost horizontal  The black ellipse is due to the very tight T constraint  ILC errors which correspond to dgL/gL=1% and dgR/gR=2% are correlated (-0.8)  Systematics are ignored so far  LHC and B physics are inaccurate for gR (ignoring T) F. Richard February

Comments  It can be shown that the SMALL residual sensitivity of B physics to ZtRtR is due to the large top mass  These comparisons are useful to evaluate the sensitivity of the various set ups but do not give the whole picture  New physics can provide additional diagrams which can influence differently the direct and indirect measurements  As an example one can have a Z’ which is not flavor diagonal and contributes to B->µµ but not to ILC couplings  At ILC a Z’ can be observed through its propagator with an effect going like ~s/M²z’ (energy dependent) F. Richard February 20159

Conclusions  A precise and model independent determination of top EW couplings requires ILC with polarised beams  The high accuracy achievable allows to reach very large BSM scales, beyond LHC (e.g. KK exchange in RS) but beware the theory errors  The T parameter seems to play a crucial part but this constraint has to be taken with a grain of salt given that it it is far from clear that the EFT formalism covers all BSM scenarios (counterexample in Little Higgs model)  B factories can add a crucial piece of information since these results also depend on loops which can be affected differently by BSM exchanges (e.g. flavour non diagonal Z’ in Bs->µµ) F. Richard February

F. Richard February BACK UP SLIDES

Expected deviations F. Richard February

Little Higgs model F. Richard February

Future F. Richard February

Ref F. Richard February

T/ 1  b F. Richard February

EFT F. Richard February